Molecular mechanisms of microbe-enhanced plant performance under nitrogen limitation

Nitrogen (N) is the most abundant and essential mineral for plants. It is a component of nucleic acids and proteins; notably rubisco for photosynthesis.

The details

As the world population gows and available arable land decreases, higher demand for crop production has come with increased use of chemical fertilizer; of which N is the major component. However, the use of N fertilizers in high input farming regions such as Europe, China and India, results in emissions and leaching. There is an urgent need to reduce nitrate leaching into groundwater.

In contrast, low input farming regions like Africa require additional N. To cope with the global N problem, plant growth-promoting rhizobacteria (PGPR) might play a crucial role as a biological fertilizer due to their ability to fix atmospheric nitrogen. Many Pseudomonas spp. have been tested as PGPR because of their distinctive traits: production of growth regulators, siderophores, volatile organic compounds (VOCs), protection enzymes, and N-fixation.

Pseudomonas koreensis has not been tested previously, so we grew it with Brachypodium distachyon under two different nitrogen conditions and phenotyped whole-plant biomass, nutrient content and protein abundance.

Under limiting N, root and shoot biomass increased in plants inoculated with P. koreensis. The root architecture was also changed: the primary seminal root decreased significantly while lateral root length increased slightly. Proteomics revealed a higher abundance of proteins associated with central N metabolism in inoculated plants grown with limiting N. A notable example was the high-affinity nitrate transporter NRT3.1 (a member of the protein family NAR2 and a dual-component transporter with NRT2.1). It appeared to be a key driving force for the improved biomass under low N.

In agreement, elemental analyses revealed a higher N content in root and shoots of plants inoculated with P. koreensis under limiting N. As expected, changes in the protein levels of central N-metabolism in Brachypodium were identified as one mode of action behind the plant growth-promotion by P. koreensis. Confirmation of phenotypes and proteomic responses remain to be tested in soil and crops. Nevertheless, these findings support the use of P. koreensis as a new PGPR to reduce the amount of chemical N fertilizer while maintaining crop biomass or yield for the future global demand.

Graduate researcher profile: Stefan Sanow

I started my PhD at the Forschungszentrum Jülich in September 2019. I received my B.Sc degree in Biology at Heinrich-Heine-University, Düsseldorf, Germany in 2016 and my M.Sc. degree in Biotechnology at FH Aachen, Campus Jülich, Germany in 2019.

Contact: s.sanow@fz-juelich.de

Supervision team

• The University of Melbourne: Professor Ute Roessner, Dr Robert Walker
• Forschungszentrum Jülich: Dr Borjana Arsova, Professor Dr Michelle Watt, Dr Silvia Schrey